N-alkylated isatins evade P-gp mediated efflux and retain potency in MDR cancer cell lines

The search for novel anticancer therapeutics with the ability to overcome multi-drug resistance (MDR) mechanisms is of high priority. A class of molecules that show potential in overcoming MDR are the N-alkylated isatins. In particular 5,7-dibromo-N-alkylisatins are potent microtubule destabilizing agents that act to depolymerize microtubules, induce apoptosis and inhibit primary tumor growth in vivo. In this study we evaluated the ability of four dibrominated N-alkylisatin derivatives and the parent compound, 5,7-dibromoisatin, to circumvent MDR. All of the isatin-based compounds examined retained potency against the MDR cell lines; U937VbR and MES-SA/Dx5 and displayed bioequivalent dose-dependent cytotoxicity to that of the parental control cell lines. We show that one mechanism by which the isatin-based compounds overcome MDR is by circumventing P-glycoprotein (P-gp) mediated drug efflux. Thus, as the isatin-based compounds are not susceptible to extrusion from P-gp overexpressing tumor cells, they represent a promising alternative strategy as a stand-alone or combination therapy for treating MDR cancer.